Molecular reaction pathways of ammonia borane dehydrogenation: Experimental and DFT elucidations

Hydrogen is a widely acknowledged clean fuel for use in PEM fuel cell (FC) vehicles, and because Ammonia Borane (AB) contains 19.6 wt.% and 175 kg/m ³ of H ₂ on a weight and volume basis respectively, it is among the best hydrogen storage materials. The detailed mechanism for hydrogen release from AB, however, is not understood. In this work, we utilize in-situ ¹¹B, ¹H NMR, TGA/MS and DFT calculations to elucidate the important reaction pathways for hydrogen release from AB. The DFT calculations are used to identify the thermodynamically favorable reaction pathways, while in-situ NMR and TGA/MS are used to confirm the presence of different intermediates. The in-situ ¹¹B, ¹H NMR analyses are utilized to obtain fundamental understanding of reaction mechanisms in different hydrogen release systems including AB hydrothermolysis and thermolysis. These techniques allow one to follow the reaction progress with time and changes in various peak areas permit the quantification of reaction kinetics. The combined experimental and DFT approaches utilized in this research provide a fundamental understanding of current hydrogen generation methods for PEM FC vehicle transportation applications.